Totals for a charity's yearly bird count

A nature charity runs a bird count once a year, over 4 days. About 60,000 volunteers record what they see in the charity's app. Each checklist holds a place, a start time and how many of each species the volunteer counted. About 250,000 checklists come in, with 3 million species counts in all.

Phones in the field often have no signal, so the app stores checklists and sends them later. If it is not sure a send worked, it sends the checklist again. About 30,000 checklists arrive in the hour after the count closes.

The public results page shows each species' total in each of 120 regions, updated during the count. Before the count, each region's experts list the species they expect there. For each one, they set the most that a single checklist should report. A count of an unlisted species, or above its limit, is held until a regional expert accepts it.

What is stored when a checklist arrives, and how are the totals on the results page built?